1. Field of the Invention
The present invention relates to a gold alloy thin wire for bonding or electrically connecting electrodes, on a semiconductor device, to external leads.
2. Description of the Related Art
Currently, circuitry wiring electrodes on a semiconductor device are electrically connected to external leads mainly by wire bonding.
The recent trend for advanced integration and function multiplication of semiconductor devices requires further miniaturization and thickness reduction of IC chips, including a need for high density packaging of semiconductor devices. To realize increase in the number of pins or terminals, the inner leads must be moved away from a silicon chip and the wire bonding span is increased. For long wire bonding spans of greater than 5 mm, it is necessary to strictly control the loop shape, including the straightness, and the reduction in dispersion. The increased number of pins also requires a reduced or refined bonding pitch or electrode interval, such as a minimum bonding pitch of 100 .mu.m or less, and thinner wires are also desired.
To achieve the increase in the number of pins and the reduction of wire pitch, efforts have been made to improve the bonding apparatus and to develop a wire having an improved looping property.
In high density packaging of semiconductor devices, for a long span of 5 mm or more, the most important problem is to prevent undesirable connection between neighboring wires and between a wire and a chip or an inner lead in order to successfully ensure the increase in the number of pins and the fine pitch. When the bonding span is increased, although various looping controls are conducted to ensure the loop height and prevent the wire dangling, loop bending unavoidably occurs more frequently upon bonding. During molding using viscous epoxy resins, the wire deforms by being swept and the sweep degree is increased with the increase in the bonding span to allow frequent occurrence of undesirable connection between neighboring wires.
The reduction in the bonding pitch also involves thinning of the wire or reduction in the wire diameter, which renders more serious the problems of the wire bend upon loop formation and the wire sweep during resin molding as can be expected from the fact that the wire strength is reduced in proportion to the square of the wire diameter. The reduced bonding pitch also requires a reduced ball size rendering it difficult to ensure the bondability of the balls.
From the view point of thinning wire and ensuring bondability, the effect of the additive alloying elements to gold alloy thin wires has been studied. For example Japanese Unexamined Patent Publication (Kokai) No. 2-119148 disclosed that Cu is an effective additive element. However, Cu must be present in an amount of 1 to 5 wt % to provide substantial effect and it is feared that such a large amount would cause a defective shape and undesirable hardening of ball. Japanese Unexamined Patent Publication (Kokai) No. 2-215140 also disclosed addition of selective amounts of Mn, Cu, and Ni in a gold wire. This only relates to suppression of formation of chemical compounds at an Au/Al joint.